Treatment of wells



Patented Apr. 6, 1954 Paul H. Gardwcll, *Tulsa, Okla, assignor to The Dow ChemicalsCompany; Midland, Mich., a cor- "partition of Delaware No'DraWing. Application August 23, 1951, Serial No. 243,351

1 Claim. l The invention relates to methods of treating earth formations. It more particularly concerns a method of treating wells in earth formations,

the earth particles of which tend to be or are carried into the Wellbor-e-by fluid produced from the earth formation.

It oftentimes happens that the bore of a well, especially one drilled for oil or gas, penetrates a producing formation some or all of the particles of whichare not held' together and retained in the formation. When production is had from such formations-the loose particles are carried by the produced-fluid into the well causing much difficulty-in its economical and efiicien't operation. The particles carried into the well are oftentimes abrasivaas whenthe particles are hard or sandy,

and readily damage the well equipment such as time to clean out the well hole and clean .or

replace the screening means to maintain .a satisfactory flow of ,fluidinto the well from the surroundingformation.

One of the objects of the invention is to provide an improved method of reducing .or preventing the passage of earth particles and the like from the producingformation into the well.

Another object is to provide an improved method'for controlling the passage ofea-rthparticles andlike sediments into thefluid-taken from the well penetrating an incompetent-or unconsolidated formation.

Still other objects and advantages will-appear as the description of the invention proceeds.

v.It lyinvention is predicated upon thed-iscovery that by .suitably treating fluid permeable earth containing or composed of particles which may be flushed from the earth by fluid produced therefrom fluid production .is obtained substantially without the usual contamination with earth solids, asby virtue of the treatment loose particles are retained in theproduction formation. v,In.adciiticu i, the resistance :to thetflow of fluid offered :by the earth formation, afterxtreatment is not seriously-affected.

Treatment according to the invention is accomplished by cementing the loose particles .one to another without completely sealing or cement ing off the interstices. .The cementing agent employed isoil and water-insoluble so that,-after cementing has been effected, fluid may be produced from the treated or adjacent formations without the usual carry-over of loose earth, rock, sand and like particles into the well, thus obviating the use of conventional screens and periodic cleaning of the well due "to sanding or sloughing.

I have found that the desired cementing action is obtained by inundating the unconsolidated formation involved with a suitably diluted partially condensed resinous liquid formed from certain mixtures of phenol and formaldehyde which on bein suitably catalyzed form'an unemulsifiecl two-phase system of a relatively small volume of a resin in situ in-the presence of the diluent. The diluent used-is soluble in the partially condensed resinous liquidmixture, as injected into the earth, but insoluble .in the hardened resin after its formation and is rejectedfrom the mixture as one-cf the two resulting continuous liquid phases in the interstices of the earth particles while the resin, which is the other of the two continuous liquid phasespgells. The gelled resin hardens around the earth "particles. The hardenedresin has a specific gravity of about 1.2, is free-from diluent, and occupies a smaller volume thanthe partially condensed resinous liquid mixture with which the formation is initially inundated. The hardened-resinforms as a continuous ;di-luent-free coating on the earth particles while the rejected resin-free diluent occupies the remainder of the interstitial :space until displaced by another fluid such as the fluid produced from the formation. The coating of the hardened resin is bonded to the earth particles and holds them togetherwvhile the diluentleaves sufficient interstitial space for fluid 'fiow. Hence, even though the interstitial space is initially completely filled with the resin-forming liquid mixture, when the formation is inundated in carrying "out a treatment, the permeability of theformation .to the flow of fluid therethroug'h, after the deposit of solid resin has formed, is not-destroyed butumay be as much as'30 to 50 per cent of the original permeability. The reduction in permeability which resultsfrom the treatment is not usually significant as in formations which by nature are loose or unconsolidated, to the extent requiring treatment "to prevent the produced fluids from carrying earth and sandparticles out of the earth, arenormally so highly 'fiuid permeable that reductions of up to 70 per cent in permeability are not disadvantageous.

The partially condensed resinous liquid mixture is formed from phenol and formaldehyde (or paraformaldehyde) and an alkaline catalyst (e. g. an alkali metal hydroxide or carbonate) in the following proportions per mole of phenol:

Formaldehyde 0.75 to 2.0 moles as HCHO. Alkali catalyst 0.015 to 0.6 mole (calculated as NaOH equivalent). Water Up to 20 moles.

The mixture is reacted, preferably at about 175 F. in a covered vented vessel at atmospheric pressure, until the viscosity, measured at 80 F., is between about 25 to 200 centipoises (cps). The reaction is exothermic and as it gets under way, it is necessary to employ cooling means to prevent the mixture from becoming overheated. After the viscosity reaches a value in the speci fied range, the mixture is acidified to a pH between about 4 and 6 and it is then allowed to settle whereupon it separates into two layers. The watery layer, which is on top, is rejected. The lower partially resinous liquid layer has a viscosity of 100 to 2000 cps. depending upon the length of the time the mixture has been reacted.

The following specific example is illustrative of the preparation of the partially resinified or condensed phenol-formaldehyde resin-forming liquid prior to dilution.

EXAMPLE 1 Mix together 390 pounds (4.15 moles) of phe- 1101, 506 pounds of 37 per cent by weight formaldehyde (6.24 moles I-ICHO), and 25 pounds of sodium hydroxide (0.625 mole) dissolved in 25 pounds of water. The total Weight of the foregoing mixture is 946 pounds and its density at 80 F. 9.3 pounds per gallon. The mixture is heated to 175 F. in a vented jacketed reaction vessel. As the reaction proceeds, cooling water is circulated in the jacket to prevent the reaction mass from becoming hotter than about 175 F. After the viscosity reaches 47 cps., the reaction mass is cooled to 80 F. Its weight is then 937.8 pounds and density 9.75 pounds per gallon. To the cooled mass is added 7.8 gallons of 32 per cent HCl (0.6 mole I-ICl) with stirring, thereby reducing the pH to and increasing the total Weight of the resulting mixture to 1013.5 pounds having a volume of 104 gallons. The acidified mixture is settled allowing the formation of two layers. The top layer which consists mainly of sodium chloride dissolved in water weighs 334.2 pounds, its density is 9.27 pounds per gallon, its viscosity 3 cps. It is rejected. The lower layer consists of 697.3 pounds of resinous liquid having a density of 10.0 pounds per gallon and viscosity at 80 F. of 230 cps. and is ready for use in the method, although, if desired, the liquid may be stored at room temperature for long periods before use without significant change. When it is desired to make a treatment of an earth formation, the diluent is added as well as the catalyst which induces hardening of the resin in situ. The resin thus hardened becomes a continuous phase free from entrapped diluent which is free to pass from the resin.

Suitable diluents are ethyl alcohol, methyl alcohol, and isopropyl alcohol, the amount (by volume) to use may be from about to 75 per cent of the volume of the partially condensed resinous liquid mixture. The diluent becomes acontinuous liquid phase (not droplets) free from resin as the resin forms and hardens in situ.

The time elapsing before hardening of the resin and good cementing action occurs on the loose particles in the formation in the presence of the diluent varies with the temperature and amount of catalyst added. In addition, the state in the transformation of the prepared resin-forming liquid into the resin in situ at which the resinification is adjudged to have reached the solid state is somewhat indistinct, because the mass generally passes from a true liquid into hard solid by degrees of chang in which the liquid passes through a semi-solid or gelled state and acquires an initial hardness which increases with time. Resins of this type may be referred to as having an initial set or gelled state as well as a final set or hard state. The time elapsing before these states are reached may be termed the initial setting and final setting times, respectively.

The amount of catalyst to add to the prepared resin-forming liquid mixture is based upon the percentage of dilution and the amount of phenol in the liquid mixture. Inasmuch as the time required for the injection into an earth formation usually varies from well to well, it is desirable to employ an amount of catalyst which will allow ample time for the majority of cases before gelation or initial hardening of the resin occurs, for example 2 hours. If more time is required for the injection somewhat less catalyst may be used and if hardening is desired sooner more catalyst may be used.

The following table sets forth the number of moles of alkali, calculated as NaOH, to use per mole of phenol in the partially condensed resinforming liquid mixture to produce gelation of the resin in situ in 2 hours at F. The gelled resin becomes hard in about 24 hours or in a length of time equal to about 12 times the gelation time.

K2003) used as the catalyst is dissolved in water to make preferably a 25 per cent solution and the solution is added to the appropriately diluted resin-forming liquid mixture in the proportions shown in the table. Intermediate proportions may be obtained by interpolation, others by extrapolation.

In applying the treatment to earth formations, such as those penetrated by the bore of a well, the amount of diluted resin-forming liquid mixture to use depends largely upon the length of the well hole adjacent to the formation to be treated. I have found that estimates of the amount of liquid needed may be made on the basis of employing about 10 gallonsof the liquid per foot of well bore of ordinary diameter, although other amounts may be used provided adequate penetration into the formation is had. Penetrations of a few inches have proved to be sufficient in many cases.

A convenient way to introduce the consolidating liquid into the formation through the well bore is to run a string of tubing into the well with a packer near the lower end, the packer being set in the hole just above the formation to be treated. After setting the packer, the requisite volume of consolidating liquid is introduced into the tubing and the liquid is preferably followed taken off production for several months.

by a cementing plug making a sliding fit in the bore of the tubing. A pressuring fluid, such as oil or water, is then introduced into the tubing behind the plug so as to forc it and the charge of consolidating liquid ahead of it down the tubing into the formation. Pressure is retained upon the tubing so as to maintain the consolidating liquid in place while the resin formed sets around the loose particles in the formation, thereby binding them in place. After the resin has formed and hardened sufficiently, the pressure is released and the tubing and packer withdrawn from the well. The well hole is then drilled out, if necessary, to clear it of resin which may have set in the hole.

EXAMPLE 2 An oil well having a casing perforated at 4708 to 4730 feet below the ground and producing therethrough became sanded up during production so that it was necessary to consolidate the formation to hold back the sand. A consolidating mixture of 50 gallons of the resin-forming liquid of Example 1 and 50 gallons of methyl alcohol was pumped into the formation through a tubing string, the lower end of which was packed off in the casing just above the perforation. After holding the injection pressure on the consolidating liquid for 24 hours, the tubing and packer were removed and the set resin in the casing drilled out. The well was then washed in with water and it started to flow. Its potential was 126 barrels of oil per day, the oil produced being sand free.

EXAMPLE 3 A cased oil well having perforations at 6349 to 6352 feet below ground was producing about 99 per cent of water, the balance being oil along with shale, gravel and sand which was carried into the well through the perforations until the well sanded up. After sanding up, the well was This well was cleaned out and then treated in similar manner to that in Example 2, using 100 gallons of the same consolidating liquid introduced in two batches of 50 gallons each. After the treatment, the well produced 50 per cent of oil and 50 per cent of water without shale, gravel, or sand, production being maintained at about 65 barrels of oil per day.

This application is a continuation-in-part of my application Serial No. 686,272, filed December 20, 1945, now abandoned.

I claim:

The method of treating an incompetent earth formation so as to cement together the loose earth particles without blocking the interstices to fiuid flow comprising cooking together phenol, formaldehyde, and an alkaline catalyst in the proportions per mole of phenol of 0.75 to 2 moles of formaldehyde, 0.015 to 0.6 mole of alkali calculated as NaOH, and up to 20 moles of water, until the viscosity of the cooked mixture measured at 80 F. is between about 25 to 200 centipoises; acidifying the cooked mixture to a pH between about 4 and 6 whereby a system of two liquids forms, one of the two liquids being a liquid resin, the other an aqueous salt solution; separating the liquid resin from the aqueous salt solution; diluting the sti-separated liquid resin with a water-soluble organic liquid selected from the group consisting of ethyl alcohol, methyl alcohol, and isopropyl alcohol in amount between about 10 and per cent by volume of the liquid resin; mixing with the resulting diluted liquid resin, as an aqueous solution, an alkali catalyst in amount between 0.024 and 0.182 mole of alkali calculated as NaOl-I per mole of phenol; introducing into the interstices of the formation to be treated the resulting alkali-containing diluted liquid resin and maintaining the same therein whil the diluted liquid resin spontaneously yields in situ both a continuous phase of solid resin and a continuous liquid phase which occupies and excludes from a portion of the interstices of the earth formation the solid resin, whereby fluid permeability of the so-treated earth formation is retained and the earth particles are cemented together by the solid resin.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 2,235,193 Balz Mar. 18, 19 41 2,366,036 Leverett et a1 Dec. 2, 1944 2,389,865 Mills Nov. 27, 1945 2,434,605 Wrightsman Jan. 13, 1948 

